The present invention is relative to a device for measuring the state of oils or fats in accordance with the generic. part of claim 1 as well as to a method for measuring the state of a measured material and to a device for carrying out the method.
Oils and fats are very important for human consumption and in particular for the preparation of foods. Thus, many foods, e.g., potatoes or foods which have already been breaded are cooked in hot oils or fats by placing them into these hot fats, which makes them accessible for human consumption. (The term xe2x80x9cfatsxe2x80x9d is intended to denote in particular a solid form of oils in this connection.) In order to cook foods the oils and fats are used in a temperature range of approximately 90xc2x0 Celsius to 180xc2x0 Celsius and more. These hot temperatures result in particular in a breakdown or change of the fat which increases more and more during the use of the oil.
This change is a degradation and takes place essentially by means of the oxidation of the oil or fat. Many chemical products are produced thereby such as, e.g., free fatty acids or polymers which not only negatively affect the taste of the prepared dishes but in particular contain substances with which can make one sick and make it necessary to replace such oils, that is, in particular frying fats, on a regular and timely basis. This replacement basically takes place according to criteria which have no direct connection with the chemical change, in particular with the harmful chemical change of the fat. The replacement takes place, e.g., after the passage of a certain time or after other irrelevant criteria. Thus, it occurs in practice that the fats are replaced too early or too late. The first instance produces unnecessary expense whereas a replacement that is too late entails the dangers cited above.
U.S. Pat. No. 3,739,265 teaches a test instrument which checks fat with a sensor to see whether it can still be used. Provision is made thereby to check the oil for its electric properties, in particular its dielectric properties. The test device comprises to this end a key-shaped carrier with a sensor arranged on its bottom which sensor is designed as a capacity sensor. To this end a certain amount of oil is placed on the sensor and the capacity measured with this system is processed in an electric circuit which yields a value- which makes a statement about the degree of degradation of the fat. In addition, a comparison is carried out between the fat or oil to be tested and a standard liquid which must also be measured in a measuring process. The change in the capacity of the sensor is a measure for the degree of degradation of the oil.
U.S. Pat. No. 5,824,889 teaches an oil sensor operating on a capacitive basis for measuring the degradation and contamination of oil. This sensor is used for checking the oil of internal combustion engines. The electric properties of the motor oil form a reference point for the degradation of the oil and for its still sufficient quality. The dielectric constant of a certain oil brand changes thereby within quite specific limits which were determined by tests and therefore yields a measurement for the degradation of the oil.
In addition, motor oil can also be degraded in its quality by other factors, e.g., by the presence of contaminants, e.g., by cooling liquids or gasoline. This can also be a measure of how far the wear on the engine has progressed and of what type it is. Since, e.g., cooling liquid has a significantly higher dielectric constant a significantly higher change of the dielectric constant can be an indication of engine wear.
The sensor described in the U.S. patent for measuring the properties of the oil of internal combustion engines comprises a sensor surface mounted in the oil, e.g., in the oil pan of a motor vehicle. Only a narrow slot is provided on the sensor which permits the passage of oil to the sensor.
The disadvantage of the first-named device is that in order to measure the oil the oil must be filled into a receiving device of an oil sensor. To this end the oil must be removed, e.g., from a deep fat flyer and introduced into the measuring receptacle of the sensor. After its electrical properties have been measured the oil is removed again and the measurement carried out with a reference oil for comparison with the first measurement. Since the oil is present thereby in a very small amount it cools off very rapidly which creates the danger in the case of fats that they become hard, which falsifies the measurement or makes it impossible.
In addition, the manipulation is problematic and the oil used for the measurement must subsequently be removed so that on the whole the process is time-consuming and unpleasant. This device is not suitable for use in practice, that is, without great expense. The device is not suitable for being used directly in the kitchen for directly checking the fat used without preparatory work.
The sensor of U.S. Pat. No. 5,824,889 is not only very bulky on account of its intended uses and not suitable for being used at various locations but it also has the disadvantage that the sensor surface has a covering which makes it difficult for the oil to reach the sensor when the sensor is used at other opportunities. In addition, it would be practically impossible to clean the sensor since this would be too expensive. In particular, this eliminates its being used in conjunction with food fats.
The present invention has the problem of suggesting a measuring device and a method of its operation which device avoids the disadvantages of the state of the art and is suitable by virtue of its easy handling and a suitable measuring method not only for being used under laboratory conditions but can be used in a very variable manner on account of its ability to be handled and operated very simply. In particular, the use of the device in accordance with the invention in the area of measurements, e.g., of frying oils or frying fats should be created without these oils or fats having to be first removed from the pan for measuring.
In addition, the invention should create a device which can be used in a flexible manner which can also be used for determining the quality of other oils, e.g., motor oil. Another target of the invention is to create a measuring device with an oil sensor which can be used in a mobile fashion, that is, without the sensor having to be permanently installed for measuring or having to be integrated in the oil container. In addition, a method should be created which yields precise results.
The design of the measuring device in accordance with the invention brings it about that a device is created which is easy to handle, manipulate and can be reliably operated even when dealing with hot liquids. In addition, it has the advantage that it supplies reliable measured results independently of the temperature of the matter to be measured and without preparatory measures being required in order to be able to use the device. The fact that the attachment is designed as a rod-shaped or tubular element brings it about in an advantageous manner that the measuring head and the housing are rigidly connected to one another so that only one hand is required for operating the measuring device. The handling of flexible cables is eliminated. A reliable handling of the measuring device is assured. In addition, the attachment makes it possible for the operator of the measuring device to be assured in an advantageous manner of a safe interval between the matter to be measured and his hand, which guides the measuring device on the housing. The connection between the measuring head and the evaluation electronics takes place in an advantageous manner via the interior of the attachment.
The designing of the measuring device with a compensator brings it about in an advantageous manner that changes of the sensor itself caused by a change in temperature are compensated. This makes it possible to use the measuring device at different temperatures in a simple and economical manner without expensive methods requiring an adjustment of the device to different temperatures being necessary.
In a particularly advantageous manner the compensator has the same design as the sensor itself This makes it especially simple and reliable to integrate the compensator into the evaluation electronics as regards the circuitry without further additional measures being necessary. In an especially advantageous manner the compensator is designed just as the sensor is. This assures a reliable statement about the state of the oil or fat. The sensor advantageously comprises two electrodes to this end of which at least one consists of a thin metal wire. The term xe2x80x9cwirexe2x80x9d in this context also denotes a printed circuit. To this end, e.g., gold is applied in the form of a circuit and subsequently fixed on the carrier plate. This can take place, e.g., by burning it in. This makes it possible in an advantageous manner to produce the sensor in a precisely reproducible manner and also to simply and reliably arrange it on a carrier.
A gold wire proved to be especially advantageous. In a quite particularly advantageous manner the carrier plate consists of a ceramic material since this material is chemically neutral and has good properties as regards thermal expansion. In addition, it has the particular advantage when the measuring device is to be used with foods such as, e.g., frying fats that ceramic material, in particular, is food-proof, that is, can be safely used with foods. It is particularly advantageous to use a material for the measuring device which is heat-resistant up to above 200xc2x0 Celsius, especially up to above 230xc2x0. This assures that the measuring device can be reliably used without being destroyed by the temperature of the material to be measured.
The measuring head advantageously comprises a cover for the sensor so that the latter cannot be destroyed by mechanical contacts. This cover is advantageously designed in such a manner that it is constructed as an edge of the attachment. This is achieved in an especially advantageous and simple manner in that the attachment is cylindrically designed and terminates with an oblique surface. This protects the sensor from contacts and at the same time makes it readily assessable in particular for cleaning measures.
In a particularly advantageous further development of the invention a display is associated with the output unit of the measuring device via which display one can optically recognize in a simple manner which parameters are set on the measuring device and what the result of measuring is. This result is displayed in an especially advantageous manner as a numeric value or graphically, e.g., as a bar graph in which case the output unit is designed in such a manner that it can be adjusted to selectively show the result of measuring.
The measuring device is advantageously designed with an evaluation electronics associated with storage means for storing, e.g., configuration data, calibration data of the measuring device or correction data. As a result thereof the measuring device can operate in a particularly exact and advantageous manner especially, e.g., by means of specific data regarding certain oils. Data from test series is integrated into the storage means thereby so that specific deviations and changes in the dielectric constants of various commercial fats and oils can be taken into account in order that the measuring device can operate in an especially precise manner.
In a particularly advantageous embodiment of the invention the evaluation and control electronics comprises a microcontroller which assures that the measuring device can operate reliably, simply, rapidly and flexibly. In particular, correction data can be managed simply and quite precisely with the aid of a microcontroller. To this end the measuring device also comprises in an especially advantageous manner an input unit for entering data and an output unit for outputting the result of measuring so that additional information can be entered into the measuring device by the operating person and that this can also be controlled, e.g., via the output unit, which creates a device which can be set and adjusted for different areas of use in a flexible manner.
For storing data the measuring device advantageously comprises an EEPROM, which makes possible a rapid and extensive storage of data. In an especially advantageous further development of the invention the measuring head additionally comprises a temperature sensor so that the device can also be used at the same time in an advantageous manner for measuring the temperature of the material to be measured. The temperature sensor and/or the measured temperature can also be advantageously used to set up correction values, if this is necessary, which can then make the result of measuring even more precise.
The design in accordance with the invention of the method for measuring the state of the material to be measured brings it about that a compensation of temperature-related changes of the measured value of the sensor can be compensated simply and reliably. As a result of the fact that the compensation takes place electronically directly in the measuring bridge expensive additional measures are not necessary. As a result thereof, the electronics is so simply designed that it corrects itself. Expensive control and regulating measures within an evaluation electronics are eliminated. As a result of the fact that the compensation unit is also advantageously designed as a capacitor the compensation is achieved in a reliable manner. In an advantageous further development of the method the compensation unit is exposed at the same time to the same temperature as the sensor itself during the measurement. This is achieved in particular in an advantageous manner in that the compensation unit is arranged on the same carrier as the sensor itself, which reliably assures that the compensator is exposed to the same temperature.
A compensation is achieved in an especially advantageous manner if the compensation unit is designed equally to the sensor. This excludes, e.g., differences in manufacture and different reactions of an electronic component due to a different spatial design. This renders the method especially simple and reliable and a device can be manufactured in an especially simple manner.
A microcontroller is used with particular advantage for controlling the measuring bridge and for detecting the values of the measuring bridge. This makes possible a fine control of the measuring bridge and detection of the results of measuring.
The device in accordance with the invention for carrying out the method assures that the method can be reliably carried out. The device is designed in an especially advantageous manner if the compensator is arranged on a carrier which, e.g., makes contact with the material to be measured in such a manner that the temperature of the material to be measured is also reliably transferred to the compensator. The device is designed in an especially simple and advantageous manner in that a carrier is used which carries the sensor on the one side and the compensator on the back side. As a result thereof both exactly determine the temperature of the material to be measured via the carrier. This makes a very precise measurement possible.
As a result of the equal construction of the capacitor and the compensator the method is reliably carried out by the device and no further measures and devices are required for achieving a compensation. The device is provided in an especially advantageous manner with a microcontroller which controls the measuring bridge in a simple, reliable and versatile manner. This microcontroller already contains analog and digital converters in an advantageous manner so that no additional components are required. The microcontroller contains direct connections which are capable of converting the analog measured value supplied by the measuring bridge directly into a digital value which can also be further processed by the microcontroller. Inversely, it is just as advantageous if the microcontroller also comprises connections at the same time which supply the control signals of the microcontroller in analog form already for controlling the measuring bridge so that they can be furnished to the measuring bridge.
In an especially advantageous further development of the invention the device in the measuring head additionally comprises a temperature sensor which creates additional information as well together with the output unit for the operating person. It is moreover possible that the temperature values of the temperature sensor from the microcontroller are used for purposes of control and compensation.